PL45 advantages: Much Faster AF 2:1 Magnification (on 35mm equivalency) Compact and Small Possibly better LOCA performance Oly 50mm F2 advantages: Weather sealed with MMF-3 1 full aperture faster Possibly better bokeh 100mm is better than 90mm Possibly slightly sharper Different review sites tend to go back and forth on which one is sharper. My guess is that they're probably pretty close and the Oly ZD might be slightly sharper. I tend to trust the DPReview site more because they have more expertise than say TechRadar or ePhotozine. However if you read Lenstip.com, the PL45 has a significant advantage (they did use an E-510 though for the ZD which is notorious for having a strong AA filter). I have to wonder who is more accurate. Right now, I'm leaning heavily on the Olympus solution because of the weather sealing primarily, full aperture stop advantage (useful for portraits), and slightly sharper reputation. The PL45mm though really gets me on the very clean LOCA and AF speed which will probably be very useful. I wonder if perhaps the Oly 50 ZD LOCA might go away as you go to F2.8 or F4. I plan to shoot this combo in the rain and snow so the weather sealing would be a big win. Then again I can just cover the PL45 in a plastic bag and it'll be sort of weather sealed as well and offer more useable AF speeds.